It is estimated that malnutrition costs the UK more than the £2bn per year attributed to obesity.

Not only does it cause health problems itself, it delays recovery from illness.

The study found that up to 60% of hospital patients were clinically malnourished.

In addition, up to 50% of patients in care or residential homes, up to 30% of patients attending outpatient clinics and GP surgeries, and up to 14% of elderly people not in hospital or care are either malnourished or at risk of malnourishment.

Patients who are malnourished when discharged from hospital are two-and-a-half times more likely to require healthcare at home.

And malnourished people are more likely to need a longer stay in hospital.

Screening tool

Definition of malnutrition

"A state of nutrition in which a deficiency, excess or imbalance of energy, protein, and other nutrients causes measurable adverse effects on tissue, function and clinical outcome."

The report says no consistent or coherent framework exists to tackle the problem.

The MAG has designed an assessment method, based on following a person's weight loss over a six-month period, to identify whether people are at risk of malnutrition.

They hope that widespread use of the technique will help to identify a greater proportion of malnourished people.

MAG head Professor Marinos Elia said: "Research shows that malnutrition is a serious public health issue in the UK and that good nutritional care can have a positive impact on health.

"It is therefore absolutely essential for us to radically improve nutritional care provision.

"In order for this to happen, all healthcare professionals - GPs, nurses, residential care staff, dieticians - need to be given the means to accurately screen, monitor, and nutritionally treat those under their care, with continuity from hospital to home and vice versa."

Rick Wilson, director of nutrition and dietetics at King's College Hospital London, said most cases of malnutrition were linked to other illnesses, which depressed patient's appetite.

He said: "If we don't spot malnutrition and treat it early enough treatments can take longer, and wound infections and other complications are more likely which is bad for the patient and bad for the health service because of the greater resources it consumes.

"We used to think that losing weight and becoming frail was a normal part of ageing, but now we recognise that it is an important part of illness and that we can intervene to stop it happening."

Mr Wilson said awareness of malnutrition was still poor among doctors and nurses.

He said one way to minimise the risk of the condition going undiagnosed would be to weigh patients every time they sought medical help, so that any signs of weight loss would be recorded at an early stage.